underwire bra

An underwire bra (also under wire bra, under-wire bra, or underwired bra) is a brassiere that utilizes a thin, semi-circular strip of rigid material fitted inside the brassiere fabric. The wire may be made of metal, plastic, or resin. It is sewn into the bra fabric and under each cup, from the center gore to under the wearer's armpit. The wire helps to lift, separate, shape, and support a woman's breasts.

(taken from Wikipedia)